Issue #18427: str.replace could crash the interpreter with huge strings.

This fixes two places where 'int'  was used to represent
the size of strings, instead of 'Py_ssize_t'.

(The issue is not present in the corresponding code in the 3.x branches)

Fixes #18427
diff --git a/Misc/NEWS b/Misc/NEWS
index c3689e9..804e8c2 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -24,6 +24,8 @@
 Library
 -------
 
+- Issue #18427: str.replace could crash the interpreter with huge strings.
+
 - Issue #18347: ElementTree's html serializer now preserves the case of
   closing tags.
 
@@ -88,7 +90,7 @@
 
 - Issue #7136: In the Idle File menu, "New Window" is renamed "New File".
   Patch by Tal Einat, Roget Serwy, and Todd Rovito.
-  
+
 - Issue #8515: Set __file__ when run file in IDLE.
   Initial patch by Bruce Frederiksen.